The wide utilization of communication devices drives the rapid development of radio frequency (RF) filters. These RF-filters are needed to protect the receive (Rx) path/transmit (Tx) path from noise and interference from different RF channels and sources. For cellular phone applications, the Rx/Tx bandwidth is relatively narrow, typically no more than 194 MHz, and the Rx band is only 190 MHz apart from the Tx band. Therefore, highly selective RF filters are required to make sure only signals from the correct Rx/Tx band are used.
In order to achieve steep filtering, surface acoustic wave (SAW) filters, bulk-acoustic-wave (BAW) filters, thin-film bulk acoustic resonator (FBAR) filters, and microelectromechanical system (MEMs) filters have been introduced because of their quality (Q) factor advantages. However, these high-Q filters normally do not have high power handling, such that only a small amount of power can flow through these high-Q filters, which is undesirable for high power communication devices.
Accordingly, there remains a need for improved filter designs to provide high Q factors without being limited to low power handling. In addition, it is also desirable that the improved filter designs have the flexibility to be used in applications in different frequency ranges.